The present invention relates to a linear motor of moving-coil type comprising a stationary part including two opposed magnet paths each having a plurality of permanent magnets arranged linearly, and a moving coil arranged in the gap formed between the two magnet paths and adapted to move linearly along the magnet paths.
A linear motor of moving-coil type for a magnetic disk is disclosed in the U.S. Pat. No. 4,396,966 as a conventional drive system for positioning the linear motor along a long stroke. Such a linear motor of moving-coil type comprises a plurality of adjacent magnets arranged longitudinally with alternate magnet poles forming alternately-changing magnetic fields in the space thereabove, and a plurality of coil units wound in a direction perpendicular to the magnetic fluxes of the magnetic field in the space and combined to make up a carriage.
In order for the above-mentioned linear motor of the moving-coil type to move continuously along a long stroke, at least two coil units are necessary, and if a higher propulsive force is to be obtained, an increased number of coil units is required.
The simplest construction of the above-mentioned system would be obtained by arranging flat coil units described in the prior art mentioned above in longitudinal direction as long as possible. Nevertheless, it is impossible to arrange the flat coil units longer than the total length of the magnets less the carriage stroke. Another type of system may comprise flat coil units can be arranged in staggered layers. In view of the fact that the electromagnetic force of the magnets acting on the coil units decreases in proportion to the square of the distance, however, this type of system involves a low motor efficiency. Specifically, the coil units of second and third layers have an electromagnetic force extremely reduced as compared with those nearest to the magnets and therefore the propulsive force of the whole carriage fails to increase in spite of the increased number of coil units.
In any of the systems mentioned above, it is a difficult problem how to obtain a high propulsive force.